Method of plating



Jan. 21, 1958 F. L. BRQWER 2,320,754

- METHOD OF PLATIYNG Fil ed Sept. 27, 1955 CO/VVfYO/i 7'RAVEL A Q l B ggw y l 3%? A 36 I gay i f ;',@,;w

TTTTTT EY Unite METHOD OF PLATING Application September 27, 1955, Serial No. 537,000

3 Claims. (Cl. 204-202) This invention relates to improvements in electroplating methods and particularly to improvements in methods that may be carried out in automatic equipment.

The invention is especially useful in electroplating chromium but the principles thereof are applicable to electroplating any metal. The primary object of the invention is to improve plating conditions by increasing the spacing between workpieces or plating racks without reducing rate of workpiece flow through the system.

One form of conventional plating machine comprises an endless conveyer track which supports a plurality of equally spaced racks for supporting the workpieces to be plated. Each rack in its travel through the machine passes the different plating tanks for subjecting the workpiece to a desired sequence of plating operations. Each tank may comprise one or more stations and at selected stations there is provided an elevator mechanism for raising and lowering the racks to immerse or remove the workpieces from the plating tank. in the movement of a rack from one station to the next there is a transfer time period and a dwell time period which together may be considered as one cycle duration.

Assume, for example, that it is desired to subject certain workpieces to three cycles duration of immersion in the plating tank. The normal way of doing this is to provide a plating tank of three stations in length and setting the machine to lower each rack at station 1 thereof and to remain lowered through stations 2 and 3 and to raise each rack upon completion of the dwell in station 3. However, this manner of operation is objectionable because the three workpieces are immersed in the plating tank at the same time and are spaced apart by only the distance between stations. This close spacing in the plating tank is undesirable because it results in bipolar efiects and uneven distribution of plated metal. The present invention is concerned with a method to avoid these disadvantages.

The method in accordance with the present invention comprises the following steps: (1) moving a plurality of equally spaced workpieces past a plating tank having a plurality of stations; (2) immersing alternate ones of said workpieces in the first N stations of said plating tank and causing the remaining ones of said workpieces to bypass the first N stations; (3) immersing the said remaining ones of said workpieces in the last N stations of the plating tank while causing the said alternate ones of the workpieces to bypass the last N stations.

If the plating duration is to be of three cycles, for example, then a plating tank must be provided which has at least seven stations. In general, for a plating duration of N cycles the plating tank must have at least 2N+l stations.

Reference is herewith made to the accompanying drawing in which Figures l to 8, inclusive, are schematic drawings illustrating the How of workpieces through the plating tank and the sequence of operation.

in the drawing the plating tank is represented by A and is divided lIliO seven equal lengths in the direction of conveyor travel, each of which represents a station. These seven stations are identified in the several figures by the numerals l to 7, inclusive, below the line representing schematically the bottom of the tank. Each rack on which work to be plated is mounted and carried past the tank A is represented by a vertical line B. Rack numbers 1 to 8, inclusive, are identified by numerals l to 8, inclusive, in the circles above the vertical line. These are numbered consecutively. Each rack may be lowered or raised by operation of an associated elevator mechanism (not shown). Assume, for explanatory purposes, that the machine has just started and that rack 1 has moved to station 1 from the right as viewed in the drawing and is lowered to immerse the workpiece in the plating solution. This represents the first cycle of operation and is shown in Figure 1. The position of the racks during succeeding cycles of operation, 2 through 8, is shown in Figures 2 through 8, respectively. Rack 1 and all other odd numbered racks remain in the lowered position through stations 1, 2 and 3. Each odd numbered rack is raised after station 3 and remains raised to bypass the remaining stations 4, 5, 6 and 7. The even numbered racks bypass stations 1, 2, 3 and 4, but are lowered at station 5 and remain lowered through stations 6 and 7. Upon completion of the dwell period at station *7, each of the even numbered racks is raised and passes from the end of the tank.

Figures 7 and 8 show the two different arrangements of the racks in the tank during operation of the machine. It will be noted that there are always four racks in the raised position and three racks in the lowered position. The racks in the lowered position are spaced at least twice the distance between adjacent stations. For example, with a system having thirty inches center to center the racks that are plating in the plating tank are at least sixty inches center to center of the carriers. By means of the present invention the advantage of increased spacing between workpieces is achieved without reducing the rate of flow through the plating machine.

No specific form of apparatus is shown for carrying out the method. Conventional forms of automatic plating equipment may be readily modified or adapted to the present invention.

While not illustrated in the drawing it will be understood that each of the racks represented by the vertical lines are cathodic in the plating bath or tank. It will be understood that anode means not illustrated in the drawing are provided to supply plating current. The workpieces on each rack are, of course, plated during the period that they are immersed in the electrolyte in the tank.

While the invention is especially advantageous in connection with the electroplating art, the principles of the invention are applicable to other related operations.

I claim:

1. Apparatus for electroplating in which each workpiece is to be subjected to plating for N cycles in a plating tank, which comprises a plating tank having 2N+1 stations, means for moving a plurality of workpieces past said stations, means for immersing alternate ones of said workpieces in the first N stations of said tank and for bypassing the remaining ones of said workpieces from said first N stations, means for immersing the said remaining ones of said workpieces in the last N stations of the plating tank and bypassing the said alternate ones of the workpieces from the last N stations, and means for applying plating current to the workpieces while they are immersed in said tank.

2. Apparatus for processing workpieces in which each workpiece is to be subjected to treatment for N cycles in a tank, which comprises a tank having 2N+l stations. means for moving a plurality of workpieces past said stations, means for immersing alternate ones of said workpieces in the first N stations of said tank and'for bypassing the remaining ones of said workpieces from said first N stations, means for immersingthe saidre: maining ones of said workpieces in' the last N-stations of the plating-tank and bypassing the said alternate ones of the workpieces from the last N stations, and means for treating the workpieces while they are immersed in said tank.

3'. Apparatus for electroplating chromium-in which each workpiece is to be subjected to plating for three cycles in achromium plating tank, which comprises a chromium plating tank having seven equally s'paceds'tations, means for moving a plurality of workpieces past said stations, means for immersing alternate-ones of said workpieces in the first three stations of said tank and for 4 p r r bypassing the remaining ones of said workpieces from said first three stations, means for immersing the said remaining ones of said workpieces in the last three stations of the plating tank and bypassing the said alternate ones of the workpieces from the last three stations, and

means for applying plating current to the workpieces while they are immersed in said tank.

References Cited in the file of. this patent 'UNITED STATES PATENTS 

1. APPARATUS FOR ELECTROPLATING IN WHICH EACH WORKPIECE IS TO BE SUBJECTED TO PLATING FOR N CYCLES IN A PLATING TANK, WHICH COMPRISES A PLATING TANK HAVING 2N+1 STATIONS, MEANS FOR MOVING A PLURALITY OF WORKPIECES PAST SAID STATIONS, MEANS FOR IMMERSING ALTERNATE ONES OF SAID WORKPIECE IN THE FIRST N STATINS OF SAID TANK AND FOR BYPASSING THE REMAINING ONES OF SAID WORK- 